Cryogenic method



June 15, 1965 s. c. COLLINS 3,188,823

CRYOGENIC METHOD Filed Jan. 19. 1961 FLOW CONTRO RECTIFYING COLUMN PRESSURE EXPANSION 5| ENGINE SURGE CHAMBERS INVENTORZ SAMUEL C. COLLINS ATTORNEY United States Patent 3,188,823 QRYUGENIC METHUD Samuel C. Collins, Belmont, Mass, assignor to Soy Manufacturing ompany, Pittsburgh, Pa, a corporation of Pennsyiyania Filed Jan. 19, 1961, Ser. No. 83,709 2 Claims. (6i. 62-413) This invention relates to cryogenic methods for the separation of components of a gaseous mixture and more particularly to the separation of gaseous components of air to provide at least one component thereof as a I substantially pure product.

As is well known, one particularly desirably manner of separating the components of gaseous mixtures is by employing cryogenic processes which operate at absolute temperatures (degrees Kelvin K.) substantially below the condensation temperature at which liquefaction or solidification of some of the components of the mixture occurs. Under such circumstances it is necessary, particularly with reference to a continuous process, that gases which condense at temperatures higher than the condensation temperature of the component desired be removed from the gaseous mixture prior to introducing simultaneously removing previously liquefied or solidified gaseous components from the other of the heat exchangers and thereafter reversing the process flow to the heat exchangers whereby their functions are reversed.

Such reversing heat exchanger processes have a disadvantage in that when the reversal of the heat exchangers occur a warming thermal shock occurs throughout the remainder of the cryogenic apparatus. Although, in the past cryogenic apparatus has been designed wherein the effect of such thermal shock does not substantially effect the operating cycle, it is the purpose of this invention to provide a process and apparatus in which the thermal effect of heat exchanger reversal is minimized and the temperatureiof the process gas as it leaves the reversing heat exchange means is maintained substantially constant.

Another diiliculty that is sometimes encountered in such cryogenic apparatus is that the temperature of the mixture stream does not fall to the proper level and as a result, a small fraction of an impurity is carried beyond the reversing exchanger and precipitated in sensitive areas, thus causing a malfunction of some element of the system.

Accordingly, one object of this invention is to provide a new and improved method for separating the components of a mixture of gases to obtain one component thereof as a substantially pure produce by means of a process in which the temperature of the flow at a desired portion of the process is maintained substantially uniform.

Another object of this invention is to provide a new and improved method for separating the components of a mixture of gases to obtain one component thereof as a substantially pure product by means of a process in which the temperature of the flow employed to cause certain gases in the incoming process air to condense is maintained substantially constant.

A specific .object of this invention is to provide a new Patented June 15, 1965 and improved apparatus for separating the components of a mixture of gases to obtain one component thereof as a substantially pure product by directing cold refrigerant fiows directly from a fractionating column to reversing heat exchange means in conjunction with another cold refrigerant flow.

These and other objects of this invention will become more apparent upon consideration of the following detailed description of a preferred embodiment thereof when taken in conjunction with the following drawing which represents a schematic view of cryogenic apparatus constructed in accordance with the principles of this invention.

The drawing schematically illustrates a cryogenic process and apparatus which is similar, except for the modification thereof in accordance with this invention, to that shown in copending application Serial No. 75,152 filed Dec. 12, 1960, by Robert W. Hughes, entitled Cryogenic Apparatus and Method, which application has been assigned to the same assignee as this invention as have all other copending applications identified herein. Accordingly, a complete description of the process and apparatus shown is not believed to be necessary as such can readily be obtained from the above-identified copending application. For the purposes of this invention it is sufficient to realize that in the cryogenic process as shown in the figure a suitable air compressor 2 receiving atmospheric air through a suitable intake connection 4 discharges compressed process air through a suitable line 6 to a suitable reversing control valve 8 whereby the process air is scquentially and alternatively directed through suitable lines 10 and 12 to suitable passageways 14 and 16 in suitable reversing heat exchangers l8 and 20. As is known, the process air flows first through one of the reversing heat exchangers 18 and 20 and thereafter it flows directly to the other so that impurities having a higher boiling point or condensation temperature than that of the product desired are solidified in the passageways 14 and 15 to prevent their being conducted through the remaining portion of the cryogenic apparatus wherein they may interfere with the operation thereof due to liquefaction or solidification therein.

Cleansed process air is continuously discharged through suitable lines 22 and 24 extending from the passageways .14 and 16, respectively, which lines 22 and 24 have suitable checkvalves 26 and 28 therein and are connected to a suitable line 30 which is also connected to a suitable rectification column 32. Inasmuch as the operation of a rectification column 32 is more fully described in the above identified copending application, description of the operation thereof is not believed to be warranted herein. It will be noted that a suitable air-oxygen mixture line 36 having a suitable flow control 38 therein exists from the bottom of the column 32 to a boiler portion 40 of the column 32. Eiiiuent or Waste gas exits from the boiler portion 40 through a suitable line which sequentially passes through a passageway 52 in a heat exchanger 54, a suitable line 56 to suitable lines 58 and 60 having suitable control means 62 and 64 therein, respectively. Lines 53 and 60 are suitably connected to lines 22 and 24, respectively, whereby the passageways 14 and 16 of the heat exchangers 18 and 20 are sequentially purged of the deposited impurities therein. During the operation of the column 32 liquid nitrogen accumulates on a nitrogen shelf 42 in the boiler portion 40 and is suitably removed therefrom by means of a suitable drain line 44 having suitable control valves 46 and 48 therein to permit such removal. A suitable rare gas bleed line 66 also extends from the boiler portion 40.

The refrigeration portion of the process and apparatus shown comprises high and low pressure portions with the low pressure refrigerant being compressed in a suitable separate refrigerant compressor or a suitable por- 1 tion of the compressor 2 so to have a high pressure warm refrigerant discharge through -a..suitable.line 70 to suitable lines" 72 and 74. .Line 74 hasva suitable control 41 .directed in counterflow heat exchange relationship. with the efliu'ent gas streamsby connecting line '72'to a suitable loop control line 84 having 'a plurality: .of suitable controls 1.9, '21, 25, v27, 23 fand. 29 therein. Line 84 'is 'suitably'-connected by suitable'lines 86 and 90 .to suitable passageways 88 and, 92 in the heatvexchang'ers 18 and 20, respectively.

Warm refrigerant exits from the passageways 88 and 92' through suitable lines 94 and.

96 having suitable control valves 98 and 100 therein, respectively, to. the line.82. In the embodiment shown .a suitablefsurge chamberl j51 is provided inthe line 82 on the'inlet side .of the expansion engine 106 havinga suitable line 53 extending therefrom whereby compressed nitrogen flows to heat exchanger 112 in which it is reduced to the liquid state in a suitable passageway- 35 and v exits therefrom throughjline '34 the otheriend of which is suitably connected .to column 32. "The line 34 has a suitable pressure regulating means 59 therein which is. adjusted'to allow to flow the maximum amountof'nitro- "genthat can be liquefied and thusutilize all refrigeration available in exchanger 112;. V V 1 r 7 'As is well known; the expansion of the warm refrig- 'erant ,in' the expansion engine 106 produces low pressure cold refrigerant which exits' from the expansion engine 106-through a suitable line 108,-having a suitable surge chamber 49 suitably connected therein, which line 108 is also 'connecte dlto one end of a suitable passageway 110 in the heat exchanger 112. ,The other end of the passageway 110 is connected to a suitable line 114 "which 'is connected to one endof a suitable passageway 116 in the heat exchanger 78. Refrigerant now at substantially room temperature exits from the passageway 116 through a suitable line 118 having asuitablecontrol valve 43thereinto 'a suitable line -102. Line 102 isconnected to the inlet connection 104 of'the refrigerant portion of the compress-or 2. A line 121 extending from. the surge chamber 49 to the engine 106 serves as a V 4. invention is betterrunderstood by describing an illustrative operating condition. It will be realized that the following data are purely illustrative and cannot be considered as the only operating conditions under which this or other cryogenic processes operate. Thus, in the nitrogen cycle shown it would be obvious that the amount of product" nitrogen desired determines the quantity of process air that 'rnust enter the system. '-Once the quantity of process air through each heat exchanger .18 and 20 is determined, the .quantity vof ,cold refrigerant required is established dependent upon the maximum allowable d ischarge' temperature for the cleansed process'air as it leaves the heat exchangers 18 and 20. The quantity of .cold refrigerant .fiow through the heat exchanger 112 which is sulficient for its function of cooling the column make up nitrogen is also determined; Thus, the total .quantity of' cold refrigerant.is determined depending on the process and the apparatus. I V

In practice for the process shown it is necessary that the temperature of the :cleansed process air as it leaves heatexchangers 18 and 20 be at or below 115 Kelvin land is preferably in a range .(inorder to .obtain a satisfactory cryogenic process) from 1l0 'l15 Kelvin. Temperatures in excess of 115 Kelvin will permit gases 'to escape to the rest of the cryogenic. apparatus which gases haveva condensation temperature higher than that ofthe nitrogen product. In practice with a given nitrogen production approximately eighty-nine moles ofcold wrefrigerant flow from the expansion engine 106 perminute with eighty moles .per minute flowingwthrough passageway 110,,nine moles per minute flowing through passageway 122 of heat exchanger 54 and eleven moles. per minute of gaseous nitrogen circuit make up flows from the column32 through line .47 and joinsin line 1124 with taining' substantially constant pressurein that end of the I engine cylinder. Cold refrigerant also flows through a sultable line 108 connected to the line 108 and to 'a suitable passageway 122 in heat'exchanger 54. Cold refrigerant exits. from the passageway 122 through a suitable line 124-;which is connected to'suitable lines 126 and 128. Lines 126 and 128 are connected to suitable passageways 7 and 9 in the heatexchangers 18'and20, respectively. throughv the passageways '7 and 9 and exits from the lines-i7 and 9 through lines 3 and 5,i respectively, which by means of suitable controls 13, 11,15 and17 are connected to the line 102 and thence to the inlet'side of the refrigerant compressor; A suitable nitrogen makeup linea47'7for the refrigerant'portion oft-he cycle is con nected between :the boiler portion of the column 32 and' the line 124. 'The operation of the cryogenic apparatus heretofore described is-i dentical to thatfully described in the aboveidentifiedLcopending application except for the result obtainedl'by using the line 47" and further descriptionthereof is not believed-to be necessary. For convenience in understanding, the same reference numerals have been used to identify identical apparatus in this and such copending application. 7 V V Although theconnection of the line 47' constitutes the novel'struct-ure of this invention, it is:believed'that this The refrigerant is warmed as it flows the nine moles flowing-from the heat exchangerv 54'to line 124;. Insuch practice the eleven moles is" atatemperature' of 94.5. Kelvin and the nine moles is at Kelvin so that'by mixing such -flows1a resultant temperature of substantially 99.5 Kelvin is obtained for thecold rerigerantfiow prior to introduction to the heatexchangers 18 and 20. This outgoing stream of nitrogen at 995 Kelvin'is capable of cooling the incoming stream of air below the allowable maximum of. Kelvin thereby -insuring condensation of the desired gaseous components 'inthe incoming process air. r 1 l [In addition to obtaining the desiredtemperature in the cold refrigerant flow as described, the use of the eleven mole flow from the column 32 stabilizes the temperature of .the cold. refrigerant flow due to the fact that the variations in operating conditions which may occur in the column '32 will,not substantially' affect the. temperature of the gaseous nitrogen flow in line ,47'. It .is known that the colun1n,32. contains a mixture ofboth liquid and gaseous nitrogen 'in the upper boiler portion 40 thereof; consequently the temperature of. the nitrogen gas isjatthe saturation temperature. 'The saturation temperature is inturndependentupon the. operating pressure of the column 32 which .in the practice described is at five atmospheres. At fiveatmospheres the saturation temperature is 94.5- Kelvin; atjfour and one-half atmospheres. the saturationtemperature is 932 Kelvin and at five and one-half atmospheres the saturation temperature is 95.7" Kelvin. Thus-unusually wide swings in pressure of the column 32-will not .substantially'aifect the exit temperature of 'the'nitrogen in :line 47". It will be realized that as the line 47' is connected to the discharge side of the expansion engine'106 the pressure in the discharge side of the expansion engine and the-column 32 will achieve 'a balance wherebyflow from 'thecolumn 32 through line 47' to the line -124 occurs.

Thus, it will be seen that this 'invention'provides, a means forstabilizing the temperature of reversing heat exchangers which can be accomplished without any additional cost-to existing cryogenic apparatus.

For the purpose of best understanding the principles of this invention, the description herein has been made with reference to utilizing atmospheric air as the process or incoming mixture of gases the components of which are separated to provide substantially pure nitrogen, however, it will be realized that the principles of this invention are applicable to the separation of one or various components from a mixture of gases. Having described a preferred embodiment of this invention in accordance with the patent statutes, it is to be realized that modifications thereof may be made without departing from the broad spirit and scope of the invention. Accordingly, it is respectfully requested that this invention be interpreted as broadly as possible and be limited only by the prior art.

I claim:

1. A method of reducing the temperature of a cryogenic fluid to a predetermined temperature by means of a gaseous stream, derived from a rectification column,

having a temperature below such predetermined temperature comprising the steps of; effecting a first reduction of temperature of said cryogenic fluid by passage thereof through an expansion engine, effecting a second reduction of temperature of said cryogenic fluid by passage thereof through a heat exchanger, and effecting a third reduction of temperature of said cryogenic fluid by mixing said cryogenic fluid with said gaseous stream after passing through said heat exchanger.

2. A method of separating the gaseous components of a mixture of gases comprising, purifying a stream of a mixture of gases containing a desired gaseous component by passing a stream of said mixture of gases in heat exchange relationship in a first heat exchange means with a second stream which second stream is composed of said desired component and has been expanded and cooled prior to being introduced into a second heat exchange means wherein said second stream is further cooled, thereafter said second stream is introduced into said first heat exchange means to reduce the temperature of said mixture so that at least one of certain gaseous components of said mixture is transformed in state with at least a portion of said transformed other component remaining with said first heat exchange means and with said desired component remaining in a gaseous state, discharging said purified stream to a rectification column wherein said desired component thereof accumulates in a saturated vapor condition, discharging a portion of said desired component from said rectification column into said expanded and cooled second stream subsequent to its passage through said second heat exchange means and prior to the flow thereof into said first heat exchange means said portion being a quantity suflicient to stabilize the temperature of said second stream.

References Cited by the Examiner UNITED STATES PATENTS 1,000,655 8/11 Wolf 62-20 X 1,840,833 1/32 Claude 6220 2,496,380 2/50 Crawford 6239 X 2,697,922 12/54 Schilling 6239 X 2,765,637 10/56 Etienne 6239 X 2,823,523 2/58 Eakin 6240 X 2,932,174 4/60 Schilling 6238 X 2,955,434 10/60 Cost 6239 X NORMAN YUDKOFF, Primary Examiner. ROBERT OLEARY, Examiner. 

1. A METHOD FOR REDUCING THE TEMPERATURE OF A CRYOGENIC FLUID TO A PREDETERMINED TEMPERATURE BY MEANS OF A GASEOUS STREAM, DERIVED FROM A RECTIFICATION COLUMN, HAVING A TEMPERATURE BELOW SUCH PREDETERMINED TEMPERATURE COMPRISING THE STEPS OF; EFFECTING A FIRST REDUCTION OF TEMPERATURE OF SAID CRYOGENIC FLUID BY PASSAGE THEREOF THROUGH AN EXPANSION ENGINE, EFFECTING A SECOND REDUCTION OF TEMPERATURE OF SAID CRYOGENIC FLUID BY PASSAGE THEREOF THROUGH A HEAT EXCHANGER, AND EFFECTING A THIRD REDUCTION OF TEMPERATURE OF SAID CRYOGENIC FLUID BY MIXING SAID CRYOGENIC FLUID WITH SAID GASEOUS STREAM AFTER PASSING THROUGH SAID HEAT EXCHANGER. 